Damping arrangement for reducing combustion-chamber pulsation in a gas turbine system

ABSTRACT

A description is given of a damping arrangement for reducing resonant vibrations in a combustion chamber ( 1 ), with a combustion-chamber wall ( 2 ), which is of double-walled design and, with an outer wall-surface part ( 22 ) and an inner wall-surface part ( 21 ) facing the combustion chamber ( 1 ), gastightly encloses an intermediate space ( 3 ), into which cooling air can be fed for purposes of convective cooling of the combustion-chamber wall ( 2 ).  
     The invention is distinguished by the fact that at least one third wall-surface part ( 4 ) is provided, which, with the outer wall-surface part ( 22 ), encloses a gastight volume ( 5 ), and that the gastight volume ( 5 ) is connected gastightly to the combustion chamber ( 1 ) by at least one connecting line ( 6 ).

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to a damping arrangement for reducingresonant vibrations in a combustion chamber, with a combustion-chamberwall which is of double-walled design, and, with an outer wall-surfacepart and an inner wall-surface part facing the combustion chamber,gastightly encloses an intermediate space, into which cooling air can befed for purposes of convective cooling of the combustion-chamber wall.

[0003] 2. Discussion of Background

[0004] A combustion chamber with a combustion-chamber wall ofdouble-walled design mentioned above emerges from EP 0 669 500 B1. Thereis a flow of compressed combustion feed air for cooling purposes throughthe enclosed intermediate space of the combustion-chamber wall ofdouble-walled design which surrounds the combustion zone, thecombustion-chamber wall of double-walled design being cooled by way ofconvective cooling. Further details of the particular configuration of acombustion chamber of this kind can be found in the abovementionedEuropean patent, to the disclosure of which explicit reference is madeat this point.

[0005] Combustion chambers constructed in this way are used primarilyfor the operation of gas turbines but are also used generally inheat-generating systems, e.g. for firing boilers.

[0006] Under certain operating conditions, noise in the form of thermalacoustic vibrations occurs in these combustion chambers and may wellshow highly pronounced resonant phenomena in the frequency range between20 and 400 Hz. Such vibrations, which are also known ascombustion-chamber pulsations, can assume amplitudes and associatedpressure fluctuations that subject the combustion chamber itself tosevere mechanical loads that may decisively reduce the life of thecombustion chamber and, in the worst case, may even lead to destructionof the combustion chamber.

[0007] Since the formation of such combustion-chamber pulsations dependson a large number of boundary conditions, it is difficult or impossibleto predetermine precisely the occurrence of such pulsations. On thecontrary, it is necessary to respond appropriately during the operationof the combustion chamber in cases of resonant vibration increases, bydeliberately avoiding combustion-chamber operating points at which highpulsation amplitudes occur, for example. However, it is not alwayspossible to implement such a measure, especially since, when starting upa gas turbine system, for example, a large number of particularoperating states have to be traversed in order to be able to reach thecorresponding optimum rated operating range for the gas turbine.

[0008] On the other hand, measures for the selective damping of resonantcombustion-chamber pulsations of this kind by means of devices, e.g.using suitable acoustic damping elements such as Helmholtz dampers orλ/4 tubes, are known. Acoustic damping elements of this kind generallycomprise a bottleneck and a larger volume connected to the bottleneck,which is matched in each case to the frequency to be damped. Especiallywhen selectively damping low frequencies, there is a need for largedamping volumes, which cannot be integrated into every combustionchamber for design reasons.

[0009] Active countermeasures are also known for selectively combatingcombustion-chamber pulsations, by means of which anti-sound fields, forexample, are coupled into the combustion chamber for the selectivesuppression or elimination of resonant pressure fluctuations.

[0010] All the initially mentioned measures for selectively dampingcombustion-chamber pulsations are matched individually to thecorresponding conditions of the individual combustion chambers andcannot readily be applied to other types of combustion chamber.

[0011] The combustion chamber described at the outset with convectivecooling within the combustion-chamber wall, which is of double-walleddesign, has been optimized in light of combustion with low pollutantemissions. With a combustion chamber of this kind, it is furthermorepossible to achieve very lean combustion using a relatively highproportion of air.

SUMMARY OF THE INVENTION

[0012] Accordingly, one object of the invention is to provide noveldamping measures by means of which effective damping ofcombustion-chamber pulsations forming within a combustion chamber of thetype described above is possible without, at the same time, permanentlyprejudicing those properties of the combustion chamber that have beenoptimized for combustion. It is especially the object to find dampingmeasures for which the design requirements entail as small aconstruction as possible so that they can be integrated in aspace-saving manner into combustion-chamber systems of theabovementioned type. In particular, this should leave open the option ofintegrating the combustion chamber into systems in which space is onlylimited.

[0013] The way in which the object underlying the invention is achievedis indicated in claim 1. Features that develop the subject matter of theinvention in an advantageous manner are the subject matter of thesubclaims and can be found in the description with reference to thedrawing.

[0014] According to the invention, a damping arrangement for reducingresonant vibrations in a combustion chamber, with a combustion-chamberwall, which is of double-walled design and, with an outer wall-surfacepart and an inner wall-surface part facing the combustion chamber,gastightly encloses an intermediate space, into which cooling air can befed for purposes of convective cooling of the combustion-chamber wall,is constructed in such a way that at least one third wall-surface partis provided, which, with the outer wall-surface part, encloses agastight volume, and the gastight volume is connected gastightly to thecombustion chamber by at least one connecting line.

[0015] The third wall-surface part supplements the combustion-chamberwall, which is of double-walled design in any case, at least locally orin sections to form a three-walled wall structure, the volume gastightlyenclosed by the outer wall-surface part of the double-walledcombustion-chamber wall and the third wall-surface part serving as aresonance or absorber volume, i.e. is constructed in such a way in sizeand shape that acoustically effective coupling of the resonance orabsorber volume—referred to below simply as absorber volume—to thecombustion chamber is provided via the connecting line, designed as aconnecting tube, between the absorber volume and the combustion chamber,making possible effective damping of combustion-chamber pulsations of aparticular frequency forming within the combustion chamber. Theparticular selection of size and shape applies also to the connectingtube itself, which must have a particular length and a particular crosssection to damp a desired frequency.

[0016] To couple the absorber volume delimited by the third wall-surfacepart acoustically to the interior of the combustion chamber, theconnecting line designed as a connecting tube projects locally throughthe intermediate space of the combustion chamber of double-walleddesign, through which intermediate space there is a flow of cooling air,and is simultaneously cooled in an effective manner by the flow ofcooling air around it. This has the advantage that there does not haveto be a separate flow of air through the connecting tube for coolingpurposes. It is also possible to prevent heating or overheating of theabsorber volume on the part of the combustion chamber through theconnecting tube, particularly because, as mentioned above, it undergoeseffective cooling. If the cooling effect on the connecting tube of thecooling air flowing around the connecting tube is nevertheless notsufficient, a selective flow of cooling air through the connecting tubecan supply the cooling effect that is lacking. This supplementarycooling effect can be accomplished either with the cooling air from theintermediate space and/or from outside the combustion chamber, e.g. fromthe plenum through an opening within the third wall-surface part. Astream of cooling air of this kind, directed through the connectingtube, should have a flow velocity of less than 10 m/s, however.

[0017] In a preferred embodiment, a multiplicity of connecting tubesconnected to corresponding absorber volumes is provided along thecombustion-chamber wall of double-walled design, preferably at thosepoints at which vibration antinodes form within the combustion chamber.Depending on the respective acoustic conditions, the number of suchdamping arrangements, each comprising the absorber volume and aconnecting tube, and their spatial configuration in terms of size andshape fundamentally determines the combustion-chamber pulsations formingwithin the combustion chamber, which are also termed thermal acousticvibrations. Fundamentally, the resonant frequency f to be damped can becalculated in the following way as a function of the absorber volume Ato be provided:$f = {\frac{c_{0}}{2 \cdot \pi} \cdot \sqrt{\frac{A}{V \cdot \left( {L + {{2 \cdot \Delta}\quad L}} \right)}}}$

[0018] where

[0019] c₀ is the speed of sound

[0020] A is the open surface of the connecting tube

[0021] V is the volume per tube on the cold side

[0022] L is the bore length of the tube

[0023] ΔL is the mouth correction at the tube

[0024] The above formula serves only as a rough guide, however,particularly because neither the mouth correction ΔL nor the speed ofsound c₀ is precisely known under the operating conditions of acombustion chamber. On the contrary, the natural frequency to be definedby the absorber and to be damped must be determined experimentally. Thearrangement of a multiplicity of individual damping elements both alongthe combustion chamber and in the circumferential direction of thecombustion chamber must also be matched individually.

[0025] It is the aim of a preferred embodiment to simplify such matchingmeasures. In this embodiment, an adjusting means which adjusts theacoustically effective volume in a variable manner within the gastightvolume is provided within the absorber volume, e.g. in the form of aram, which variably reduces or increases the acoustically effectivevolume. The term “acoustically effective volume” is to be understood asthat part of the absorber volume which is freely accessible to theconnecting tube. If the adjusting means designed as a ram divides theabsorber volume into two spatial zones, i.e. into a spatial zone infront of and a spatial zone behind the ram surface in relation to theconnecting tube, the volume component behind the ram surface does notcontribute anything to acoustic absorption or damping.

[0026] It is also advantageous in this context to make the thirdwall-surface part delimiting the absorber volume elastic in order tofurther improve the degree of damping of the arrangement.

[0027] The double-walled combustion-chamber wall is composed in a mannerknown per se of two wall-surface parts, which can both be produced byway of a casting process. For the exact mutual spacing of the twowall-surface parts, the inner wall-surface part provides so-calledlongitudinal ribs as spacing elements and holding ribs as fixing webs,by means of which the two wall-surface parts can be connected firmly toone another while maintaining an exact spacing. To avoid furthercomplicating the casting process and indeed to simplify it, theconnecting lines designed as connecting tubes are provided along aholding rib, which is provided in any case, enabling the connecting tubeand the holding rib to be produced as a one-piece constructional unittogether with the inner wall-surface part in a single casting step. Thismeasure furthermore makes the production, by casting, of the innerwall-surface part with an exactly specifiable wall-surface thicknessconsiderably easier, thereby making it possible to achieve large-areawall-surface parts with specifiable constant dimensioning withoutdeviations in thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] A more complete appreciation of the invention and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

[0029]FIG. 1 shows a cross section through a double-walledcombustion-chamber wall with an additional resonance absorber,

[0030]FIGS. 2a, b, c show cross sections intended to illustrate anembodiment in a multiplicity of individual absorber units arrangedadjacent to one another,

[0031]FIG. 3 shows a schematic representation of an absorber volume witha ram arrangement, and

[0032]FIG. 4 shows a schematic representation relating to thearrangement of absorber units along a combustion chamber.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Referring now to the drawings, wherein like reference numeralsdesignate identical or corresponding parts throughout the several wiews,FIG. 1 shows a cross-sectional representation of a damping arrangementfor reducing resonant vibrations in a combustion chamber 1 surrounded bya combustion-chamber wall 2, which is of double-walled design and, withan outer wall-surface part 22 and an inner wall-surface part 21,gastightly surrounds an intermediate space 3, into which cooling air canbe fed for purposes of convective cooling of the combustion-chamber wall2, in particular of the inner wall-surface part 21.

[0034] Provided on the opposite side of the outer wall-surface part 22from the combustion chamber 1 is a third wall-surface part 4, which,with the outer wall-surface part 22, encloses a gastight volume,referred to as the resonance or absorber volume 5. Via a connecting line6 in the form of a connecting tube, the absorber volume 5 is connecteddirectly to the combustion chamber 1 and simultaneously forms anacoustic operative connection between the combustion chamber 1 and theabsorber volume 5.

[0035] For acoustically effective damping of combustion-chamberpulsations, which occur at certain frequencies within the combustionchamber 1, the geometric variables of the connecting line 6 and of theabsorber volume 5 must be adapted individually.

[0036] The inner and outer wall-surface part 21 and 22 are manufacturedin a manner known per se by a casting technique, the wall-surface part21 having longitudinal ribs 7, which serve as spacer elements and whichensure an exact predetermined spacing between the outer wall-surfacepart 22 and the inner wall-surface part 21. The inner wall-surface part21 furthermore usually has holding ribs 8, which are made longer thanthe longitudinal ribs 7 and, in the assembled condition, project througha corresponding opening 9 within the outer wall-surface part 22 and arefirmly connected to the wall-surface part 22 by means of a gastightwelded joint 10. The connecting line 6 provided for the acousticcoupling of the absorber volume 5 to the volume of the combustionchamber 1 is advantageously integrally combined with the holding rib 8,which is connected integrally to the inner wall-surface part 21 justlike the longitudinal rib 7 and can be produced as part of a singlecasting process.

[0037]FIGS. 2a to c show partial views of a preferred implementation ofthe damping arrangement according to the invention. FIG. 2a shows theplan view of the outer wall-surface part 22 of a combustion chamber withlocally applied absorber volumes 5, each of which is bounded by a thirdwall-surface part 4.

[0038]FIG. 2b shows a sectional representation, along line of section AAin FIG. 2a, along the double-walled combustion-chamber wall 2 and thethird wall-surface parts 4, each of which is firmly and gastightlyconnected to the outer wall-surface part 22. Each individual absorbervolume 5 covers a connecting line 6, which establishes an acousticallyeffective connection between the absorber volume 5 and the combustionchamber 1.

[0039]FIG. 2c shows a sectional representation along line of section BBin FIG. 2b, which shows a cross section through the combustion-chamberwall 2. The individual absorber volumes 5 delimited by the thirdwall-surface part 4, each of which gastightly covers a connecting line6, are clearly visible.

[0040] It is, of course, also possible to cover both immediatelyadjacent connecting lines 6 by means of a single third wall-surface part4 only, the effect being that two or more connecting lines 6 projectinto one and the same absorber volume 5. Such a measure can be selectedaccording to acoustic conditions.

[0041] In a preferred embodiment in accordance with FIG. 3, an adjustingmeans 11 of ram-type design, by means of which the acousticallyeffective volume 5′ can be infinitely varied by appropriate linearmovement (see double indicating arrow), can be provided within theabsorber volume 5 to allow easier individual adaptation of the acousticdamping behavior of the damping arrangement designed in accordance withthe invention to the respectively occurring combustion-chamberpulsations. The acoustically effective volume 5′ is connected to thecombustion chamber 1 by two connecting lines 6 and, in this way, canselectively damp certain combustion-chamber pulsations formed within thecombustion chamber 1 according to their frequency.

[0042] To enhance damping performance, a multiplicity of connectinglines are preferably provided along the combustion chamber within thedouble-walled combustion-chamber wall. The connecting lines arepreferably to be provided at precisely those points of the combustionchamber at which vibration antinodes occur. In FIG. 4, the correspondingconnecting lines 6 to these are provided within the combustion-chamberwall 2 at those points on the longitudinal axis x of the combustionchamber at which combustion-chamber vibrations of different frequenciesf1, f2 have amplitude maxima. Depending on acoustic damping capacity,one or more connecting lines 6 can be combined in a common absorbervolume 5.

[0043]FIG. 4 also reveals that only one particular frequency can bedamped effectively,by each absorber volume. To damp two differentfrequencies f1 and f2, two differently constructed absorber volumes arerequired. The absorber volumes, which each damp vibrations of onefrequency, are preferably arranged axially in series on thecombustion-chamber housing. The absorber volumes, each for dampingdifferent frequencies, are thus distributed in the circumferentialdirection of the combustion-chamber housing.

[0044] Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

1. A damping arrangement for reducing resonant vibrations in acombustion chamber, the damping arrangement comprising: a double-walledcombustion-chamber wall defining a combustion chamber and having anouter wall-surface part and an inner wall-surface part facing thecombustion chamber, the outer wall-surface part and the innerwall-surface part gastightly enclosing an intermediate space into whichcooling air can be fed for convective cooling of the combustion-chamberwall; at least one third wall-surface part which cooperates with theouter wall-surface part to enclose a gastight volume; at least oneconnecting line; and wherein the gastight volume is connected gastightlyto the combustion chamber by the at least one connecting line.
 2. Thedamping arrangement as claimed in claim 1, wherein the thirdwall-surface part is positioned on an opposite side of the outerwall-surface part from the combustion chamber and encloses the gastightvolume with said outer wall-surface part.
 3. The damping arrangement asclaimed in claim 1, further comprising: at least one spacer element; andwherein the third wall-surface part is connected to the outerwall-surface part directly or indirectly via the at least one spacerelement.
 4. The damping arrangement as claimed in claim 1, wherein thedouble-walled combustion-chamber wall includes longitudinal, holding, orboth, ribs for the exact spacing, mutual fixing, or both, of the innerwall-surface part and the outer wall-surface part; and wherein the atleast one connecting line is positioned at the location of thelongitudinal, holding, or both, ribs and is constructed as aconstructional unit with the longitudinal, holding, or both, ribs. 5.The damping arrangement as claimed in claim 4, wherein the longitudinal,holding, or both, ribs are integrally connected to the innerwall-surface part by casting.
 6. The damping arrangement as claimed inclaim 1, wherein each at least one connecting line comprises aconnecting tube that projects through the intermediate space and isconfigured and arrange to have cooling air flowing around the connectingtube.
 7. The damping arrangement as claimed in claim 1, wherein thegastight volume comprises a Helmholtz resonator the acousticallyeffective volume of which is selected based on the acoustic damping of avibration with a resonant frequency f occurring within the combustionchamber.
 8. The damping arrangement as claimed in claim 7, furthercomprising: adjusting means for variably adjusting said acousticallyeffective volume, positioned within the gastight volume.
 9. The dampingarrangement as claimed in claim 8, wherein the adjusting means comprisesa ram, movably arranged within the gastight volume.
 10. The dampingarrangement as claimed in claim 1, wherein the third wall-surface partis elastic.
 11. The damping arrangement as claimed in claim 7, whereinthe at least one connecting line is arranged at a location relative tothe combustion chamber at which an acoustic vibration to be damped hasan antinode.
 12. The damping arrangement as claimed in claim 1, whereinthe combustion chamber is integrated into a heat- or energy-generatingsystem.
 13. The damping arrangement as claimed in claim 1, wherein thecombustion chamber comprises a gas-turbine combustion chamber.
 14. Thedamping arrangement as claimed in claim 10, wherein the at least oneconnecting line is arranged at a location relative to the combustionchamber at which an acoustic vibration to be damped has an antinode.